(define (expmod-or-zero base exp m)
  (define (one-to-zero n)
    (if (= n 1) 0 n))
  (define (test n m)
    (if
      (or (= n (- m 1))
          (= n 1))
      (remainder (square n) m)
      (remainder (one-to-zero (square n)) m)))
  (cond ((= exp 0) 1)
        ((even? exp)
         (remainder
           (test (expmod-or-zero base (/ exp 2) m) m)
           m))
        (else
         (remainder (* base (expmod-or-zero base (- exp 1) m))
                    m))))

(define (miller-rabin n)
  (define (try-it a)
    (= (expmod-or-zero a (- n 1) n) 1))
  (try-it (+ 1 (random (- n 1)))))

(define (miller-rabin-prime? n times)
  (cond ((= times 0) true)
        ((miller-rabin n) (miller-rabin-prime? n (- times 1)))
        (else false)))